'LGT' Construction Diary

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Hi,

Sound travels slower through an absorptive material, so the relative phase would change. Quite how much delay there is I couldn't tell you. I know of someone who did some measurements but in the end it was pretty inconclusive, except that there was a small delay.

Add that to the change in amplitude and you will have an effect on the vertical dispersion.

I'm sure I have an email somewhere with Aleksandar explaining what the foam did exactly and it was along those lines but I can't find it.
 
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Joined 2004
We all know open cell foam will attenuate/absorb from a given frequency and upwards depending upon its thickness. If we look at the RAAL's foam pads we can see a distinctive profile. This profile gradually increases in thickness towards the extreme length of the ribbon thus attenuating progressively more of the high frequency content as you move towards these extremes. The effect of this is concentrating the high frequencies toward the center of the driver and allowing the lower end of the frequency spectrum that the driver covers to pass virtually unaltered.

This all contributes to shaping the vertical dispersion beyond that of a normal ribbon.
 
Pink ribbon tweeters in a white and black speaker.. OH YES!!!


So, after going through all my emails from RAAL I found the info I remeberd reading, on the website - Duh! :rolleyes:

"The dispersion pads are working as an acoustic lens, by slowing down the velocity of sound and thus shaping the sound wave front from cylindrical to spherical. The parasitic effect of partial sound absorption is inevitable, but acceptable. The pads are magnetic and they can slide on the front plate. By adjusting the distance between the pads, sliding them toward or apart each other, it is possible to shape the on-axis linearity vs. wide angle vertical polar response. In this way anyone can adjust the high frequency output by his-hers own liking. If the pads are completely removed, 15 kHz on-axis response is increased in level of about 7 dB."
 
Shin:

Have you recently had some really positive experiences with ribbon tweeters that helped you make this decision or are you going for something completely new? I actually don't ever think I've heard a system using ribbon tweeters, but after reading the information of Zaph's website where he reviewed a good number of them my initial reaction to them is "why?". Respectfully, Zaph did not review the tweeter you are talking about using and I really don't know anything about it in particular.
 
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Joined 2004
m0tion said:
Shin:

Have you recently had some really positive experiences with ribbon tweeters that helped you make this decision or are you going for something completely new? I actually don't ever think I've heard a system using ribbon tweeters, but after reading the information of Zaph's website where he reviewed a good number of them my initial reaction to them is "why?". Respectfully, Zaph did not review the tweeter you are talking about using and I really don't know anything about it in particular.

John is an invaluable resource to our community, his driver tests, simply put, are amongst the best on the web. I have a ton of respect for all that effort and hardwork. But I also hope he doesn't mind me saying that he hides behind his objectivity. He's a straight down the line guy who says what he see's and plays his subjective cards very close to his chest. What he tends to forget is that sometimes people like distortion if it plays into the hands of the listener. I can live in either camp - I like my measurements but wouldn't cut my nose off to spite my face if you see what I mean. What I think we'd both agree on is that implementation makes all the difference above and beyond the drivers.

There's enough anecdotal evidence to suggest that ribbons do work and have been around every bit as long as the pistonic variants. Had they not been upto scratch they'd have died out long ago.

A driver which John would no doubt find to measure well (if he'd tested it) would be the Scan R29 I used in my last project. I was never really that impressed by it myself and always felt it was the weak link. I'm quite sure it would 'look' better than the RAAL on the test bench though.

BTW I've only heard one true ribbons - the AC G1 in a pair of commercial floorstanders called the Harmony, very nice too. I have however heard and worked with the more common planer types which I don't really have anything good or bad to say about.
 
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Joined 2004
m0tion said:
Would you mind editing your drawing to show metrics for size and perhaps a side view? Sorry for the bother, but I'm very interested in this project.

I'm still working away on some diagrams with dimensions. I'll post those when finished.

I keep playing around with the overall shape of the speakers when viewed from the side but this is my favourite so far and the one I'll likely go with unless I get some inspiration between now and finishing the final cutting list.

An externally hosted image should be here but it was not working when we last tested it.
 
Actually I find this project so completely interesting that I would really enjoy seeing any kind of documentation or notes that you use to complete it. I don't know if this suits your building habits or not, but if it's convenient I'd really enjoy seeing some photos of how you construct this beast. I know that we periodically saw shots of your other projects at various stages of completion, but it would be really great if there were photos that helped explain how you tackled certain construction complications (for instance, all of the odd angles these cabinets will have). Anyways, I know thats a lot of ask, but I think lots of people could benefit from it.
 
diyAudio Member
Joined 2004
m0tion said:
Shin:

If you wouldn't mind :). When you finish your cut list would you make it available? This is an extremely impressive and ambitious cabinet design.

Also, am I seeing correctly that you plan to alter the RAAL faceplate? Any idea how you will accomplish this?

No problem on the cutting list, I'll add a little detail on the overall construction too since its sometimes difficult to see how something would be done from a rough 2d sketch such as those I've already shown.

The faceplate will be a small custom job by Aleksander(of RAAL). He charges a small fee for this but in return you can provide him with a Coreldraw scale sketch of what you want and he'll cut accordingly. If you like I can provide you with the CorelDraw diagram I've already done.
 
diyAudio Member
Joined 2004
m0tion said:
Actually I find this project so completely interesting that I would really enjoy seeing any kind of documentation or notes that you use to complete it. I don't know if this suits your building habits or not, but if it's convenient I'd really enjoy seeing some photos of how you construct this beast. I know that we periodically saw shots of your other projects at various stages of completion, but it would be really great if there were photos that helped explain how you tackled certain construction complications (for instance, all of the odd angles these cabinets will have). Anyways, I know thats a lot of ask, but I think lots of people could benefit from it.

If you have LEAP I have some modelling done using manufacturers data. Its not really very ideal though but just gave me a rough idea of what to expect and how things will work together. Will be much better once the drivers arrive, have them mounted in the final enclosures and then measure to work through the XO details.

I always take a fair few photo's during the course of building so can extend that a little to show the more important steps without any bother.
 
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